My feeling is don’t! IMHO the weight loss window has closed and it is way too late for significant weight loss without serious risk to your fitness. Especially on such a long race, you want to be resilient, which means 1–2 extra kilos might actually help you rather than hurt you.
Maybe you could aim for 1–1.5 kg, but 3 kg is out of the question. Honestly, I’d still focus on nailing your workouts, sleep and your recovery.